In many applications for dispensing of flowable materials, and liquids, it is required to be able to start and stop the dispensing action many times. Many dispensers or applicators of flowable materials provide some form of shut-off valve, but these are often of only limited application. In many cases, the valves in such dispensers are not efficient even working under optimum conditions. Even after the valves are shut off, residues of material will cling to the nozzle, or drip on to the workpiece or machinery. With thicker, more viscous materials or liquids, the problem becomes more aggravated. With many designs of shut-off valves, even after the valve has been closed, the material or liquid strings out from the nozzle, or clings to the nozzle, resulting in the placement of an inaccurate deposit of the material on the workpiece, or leaving material from the dispensing head, stringing to the machinery or to the workpiece, in places where it is not required.
While a wide variety of viscous materials and liquids may require dispensing in this way, the dispensing of adhesives and bonding agents presents these problems in a particularly acute form. In order to overcome these problems, operators must continually wipe the tip of the dispenser in a manual operation. Automatic equipment exists for wiping the nozzle each time the valve shuts off flow. This wiping device, which is sometimes in the form of a roll of paper, will eventually be discarded after use. This can present a problem of hazardous waste, if the adhesive material is harmful, and may present significant design problems in the design and operation of the dispensing machinery.